In certain communication systems, such as in a code division multiple access (CDMA) cellular system as defined by interim specification (IS) IS-95, a receiver in the communication system determines an estimated encoding rate for each received frame. In such systems, the accuracy of the estimated encoding rate affects speech quality since any rate determination error typically causes annoying artifacts in the decoded speech signal.
In prior arts, several methods of determining estimated encoding rate have traditionally been proposed. However, when the estimated encoding rate is based on a calculated total metric information of the received frame, the estimated encoding rate very often is inaccurate and inconsistent. A calculated total metric information of a received frame may be biased by an unknown amount. The amount of bias is unknown because the environments through which the signal has propagated, demodulated and decoded have varying and unpredictable effects on the total metric information. As a result, the estimated encoding rate based on a biased total metric information becomes to some degree inaccurate and inconsistent. Inaccuracy and inconsistency in the estimated encoding rate cause annoying artifacts in the decoded speech signal.
Accordingly, there exists a need for an improved apparatus and method for performing rate determination in a communication system.